The present invention relates generally to a multiple-use needle-free (or needle-less) hypodermic jet injection devices, and to methods of reliably delivering the drug through the skin. More particularly, this present invention relates to such a device and to such method which provide an indication that the skin was sufficiently pierced by the jet to ensure that the drug was delivered. The indication is provided through measurement of the impedance.
Needle-less or needle-free hypodermic jet injection devices have been in commercial use for over 30 years. Various needleless hypodermic injection devices have been known and used in the past. These devices, also known as jet injectors, typically use highly accelerated jet of liquid moving sufficiently fast to pierce through the skin and enter the underlying tissues. The advantages of needleless devices are: generally less painful experience for patients, absence of needle-pricks, decreased probability of introducing infection, high throughput when delivering vaccinations.
The related technology includes a number of teachings, including:
U.S. Pat. No. 4,596,556, issued Jun. 24, 1986 to J. Thomas Morrow, et al.;
U.S. Pat. No. 4,913,699; issued Apr. 3, 1990 to James S. Parsons;
U.S. Pat. No. 5,730,723, issued Mar. 24, 1998, to Thomas P. Castellano, et al.;
U.S. Pat. No. 6,585,685, issued Jul. 1, 2003 to John Lawrence Staylor, et al.; and
U.S. Pat. No. 6,689,093, issued Feb. 10, 2004, to Sergio Landau. WIPO publication WO 97/37705 also discloses a disposable needle-less hypodermic jet injector.
Each of these devices has limitations, deficiencies, or disadvantages, as will be apparent in view of the following detailed description of the present invention. One of the problems of these devices is that the characteristics of needleless or jet injections typically vary with the pressures exerted by the injection device, and the nozzle diameter. The main problem of these devices is related to the significant variability of patient's size, age, sex, and weight, the nature of the injection site, and the viscosity of the injectant. Especially the patient factors variability is critical as epidermis properties vary widely across the population and are affected by gender, age, race, weight, body fat, skin conditions, and other variables. The unresolved problem of prior art is overcoming this inherent variability and guaranteeing that the outer layer of skin, stratum corneum, was sufficiently pierced and the drug was delivered through that layer. Since there is no confirmation that the skin was sufficiently pierced, very high pressure jets are typically selected, which results in more painful drug delivery and unnecessary deep penetration for person with thinner skin. Still there is no absolute certainty that the drug was delivered, putting patient's treatment at risk.
Thus there is a need in improving the control of needleless drug delivery and ensuring that the stratum corneum was sufficiently pierced during application of needleless drug delivery device.